The present invention relates to an electric motor using permanent magnets for the magnetic field, and particularly to an electric motor for driving an air conditioner and to a method of controlling the motor, and to an electric motor in which a rotor of the electric motor is comprised of a first field magnet and a second field magnet, positions of the magnetic pole centers of the first field magnet and the second field magnet being varied according to a direction of torque, effective magnetic flux density being capable of being changed according to the rotating speed, and to a method of controlling the electric motor.
In a permanent magnet field type electric motor of the prior art, an induced electromotive force E is determined by a constant magnetic flux "PHgr" generated by a permanent magnet arranged in a rotor and a rotating angular speed xcfx89 of the motor. That is, when the rotating angular speed xcfx89 (rotating speed) of the motor is increased, the induced electromotive force is proportionally increased.
Accordingly, high torque can be obtained in a low speed range, but operation in a high-speed range is difficult because the variable range of rotating speed is narrow. Therefore, it may be considered that the high-speed operation range is widened using a field weakening control technology.
Further, in an air conditioner, defrosting operation is periodically performed during heating operation. However, there is a problem in that heating capability is lowered when the defrosting operation time is long.
The method of widening the high speed operation range using the field weakening control technology described above has limitations of heat generation and efficiency decrease due to weakening field current.
Further, it is preferable that the defrosting operation during heating operation is performed at a high speed operation because the load of defrosting operation is low, but there is a limitation in the field weakening control due to the increase in the induced electromotive force of the permanent magnet.
An object of the present invention is to provide an air conditioner comprising a permanent magnet electric motor which has a high output power characteristic in a cooling and heating range and a high output characteristic even in defrosting operation in a high-speed range.
In the present invention, an air conditioner comprising a refrigerating cycle composed of at least a compressor; an electric motor to be used as a power source of the compressor; an electric driving circuit (an inverter) for driving the electric motor; an in-room heat exchanger; an electrically operated expansion valve; and an out-room heat exchanger, a flow rate of a refrigerant circulating in the refrigerating cycle being controlled by changing rotating speed of the electric motor and an opening degree of the electrically operated expansion valve, wherein
The electric motor comprises a stator having a primary winding and a rotor having a field magnet, the field magnet comprising a first field magnet having different polarity magnetic poles sequentially arranged in a rotating direction and a second field magnet having different polarity magnetic poles sequentially arranged in a rotating direction, the second field magnet being capable of rotating relative to the first field magnet, the first and the second field magnets being opposite to magnetic poles of the stator; and a mechanism for changing a phase of a composite magnetic pole of the first and the second field magnets with respect to the magnetic pole of the first field magnet depending on a direction of torque, the mechanism for changing depending on a direction of torque comprising means for making magnetic pole centers of equal-polarity of the first and the second field magnets in phase by a direction of torque generated in the rotor and by balance of magnetic action forces between the first and the second field magnets; and means for making the magnetic pole centers of the first and the second field magnets out of phase when the direction of torque generated in the rotor is reversed.